In-column particle filter

Abstract

Systems, components, and methods are described for protecting a charged particle detector against damage. A filter can include a frame and a membrane of carbon material. The membrane can define a first surface, a second surface opposing the first surface, and an aperture extending through the membrane from the first surface to the second surface. The frame can be configured to couple with a charged particle detector disposed in a charged particle beam column, the charged particle detector defining an absorption surface oriented toward the first surface. The filter can be configured to shield the absorption surface from particles incident on the second surface. The particles can include electrons, ions, or photons.

What is claimed is: 
     
         1 . A filter, comprising:
 a frame; and   a membrane of carbon material, coupled with the frame, the membrane defining a first surface, a second surface opposing the first surface, and an aperture extending through the membrane from the first surface to the second surface,   wherein:   the frame is configured to couple with a charged particle detector disposed in a charged particle beam column, the charged particle detector defining an absorption surface oriented toward the first surface; and   the filter being configured to shield the absorption surface from particles incident on the second surface, the particles comprising electrons, ions, or photons.   
     
     
         2 . The filter of  claim 1 , wherein the carbon material comprises carbon nanotubes. 
     
     
         3 . The filter of  claim 1 , wherein the carbon material comprises a layer of nonwoven carbon nanotube felt. 
     
     
         4 . The filter of  claim 1 , wherein the membrane comprises multiple substantially planar layers of carbon material. 
     
     
         5 . The filter of  claim 1 , wherein the membrane is supported over at least a portion of the membrane by a support material. 
     
     
         6 . The filter of  claim 1 , wherein the charged particle detector is disposed in a polepiece of the charged particle beam column. 
     
     
         7 . The filter of  claim 1 , wherein the charged particle detector is a mirror detector including a mirror electrode, and wherein the frame is configured to couple with the mirror detector. 
     
     
         8 . The filter of  claim 7 , wherein the mirror electrode defines a first end and a second end, the first end being proximal to the absorption surface, and wherein the frame is configured to be disposed proximal to the second end of the mirror electrode and external to the mirror detector. 
     
     
         9 . The filter of  claim 7 , wherein the mirror electrode defines a first end and a second end, the first end being proximal to the absorption surface, and wherein the frame is configured to be disposed in the polepiece, proximal to the first end of the mirror electrode and internal to the mirror detector. 
     
     
         10 . The filter of  claim 7 , wherein the charged particle detector and the mirror electrode are disposed along a beam axis, and wherein the frame is disposed on the beam axis between the charged particle detector and the mirror electrode. 
     
     
         11 . The filter of  claim 1 , wherein the frame is offset from the absorption surface. 
     
     
         12 . The filter of  claim 1 , wherein the frame comprises an electrically conductive portion, electrically coupled with the membrane and with a voltage source via a bias circuit. 
     
     
         13 . A charged particle beam system, comprising:
 a chamber, configured to receive a sample and to maintain a controlled environment in a vicinity of the sample;   a charged particle beam column, coupled with the chamber and oriented toward the vicinity of the sample;   a charged particle detector, disposed in the charged particle beam column, the charged particle detector defining an absorption surface;   a particle filter, comprising:   a frame, coupled with the charged particle detector; and   a membrane of carbon material, coupled with the frame, the membrane defining a first surface, oriented toward the absorption surface, a second surface opposing the first surface, and an aperture extending through the membrane from the first surface to the second surface, wherein the filter is configured to shield the absorption surface from particles incident on the second surface, the particles comprising electrons, ions, or photons.   
     
     
         14 . The charged particle beam system of  claim 13 , wherein the frame comprises an electrically conductive portion, electrically coupled with the membrane and with a voltage source via a bias circuit. 
     
     
         15 . The charged particle beam system of  claim 14 , further comprising:
 control circuitry, operably coupled with the bias circuit; and   one or more machine readable media storing instructions that, when read by a machine, cause the control circuitry to perform operations including applying a negative bias to the membrane via the electrically conductive portion, wherein the negative bias corresponds to a lower energy cutoff of the particle filter, below which electrons directed toward the second surface are repelled.   
     
     
         16 . The charged particle beam system of  claim 14 , further comprising:
 control circuitry, operably coupled with the bias circuit; and   one or more machine readable media storing instructions that, when read by a machine, cause the control circuitry to perform operations including applying a positive bias to the membrane via the electrically conductive portion.   
     
     
         17 . The charged particle beam system of  claim 16 , wherein the positive bias has a magnitude such that electrons incident on the second surface are characterized by an average energy above a threshold of transmissivity of the membrane for electrons. 
     
     
         18 . The charged particle beam system of  claim 13 , wherein the charged particle detector comprises a conductive material disposed over at least a portion of the absorption surface, wherein the charged particle detector is electrically coupled to a voltage source via a bias circuit, and wherein the charged particle beam system is configured to apply a bias voltage to the conductive material via the bias circuit. 
     
     
         19 . The charged particle beam system of  claim 13 , wherein the charged particle detector is a mirror detector including a mirror electrode, and wherein the frame is configured to couple with the mirror electrode or to be disposed between the mirror electrode and the absorption surface. 
     
     
         20 . The charged particle beam system of  claim 13 , wherein the membrane comprises multiple substantially planar layers of carbon nanotube material.